The present invention is broadly directed to actuator mechanisms and, more particularly, to embodiments of a ball and piston rotary actuator mechanism using linear actuators to pivot a first structure relative to a second structure.
Many robotic devices utilize robotic arms or arm like structures (herein generally referred to as arms) for conducting work at a site of use. Often such robotic arms are utilized in environments which are dangerous or hazardous to humans, such as deep sea construction or exploration, chemical or explosives handling, outer space construction and the like. An example of such use of robotic arms is described in U.S. Pat. No. 4,648,782, which is incorporated herein by reference.
A robotic arm generally includes an elongated arm member which is pivotally connected to another structure, such as a support base or another robotic arm member. Some sort of motor is engaged between the arm member and the other structure to cause relative pivotal movement therebetween. The type of motor used depends on the intended function of the robotic arm. For high torque applications, it has been common to provide parallel sets of push/pull hydraulic cylinder arrangements which linearly move a rack gear engaged with a pinion gear secured to a shaft to which another arm is attached. One problem with such an arrangement is that one set of cylinders typically projects from the end of the arm. In some situations, such projecting cylinders can limit range of motion of the attached arm and are also vulnerable to damage by unintended contact with other structures.
Another approach to robotic arm articulation has involved vane motors. A vane motor typically has an annular chamber in fluid pressure between a fixed vane member and a movable vane connected to a shaft causes the movable vane to move thereby applying torque to the shaft. A problem with vane motors is a rotary stroke of less than 360 degrees because of space taken up by the fixed and movable vanes. In some robotic applications, a pivot range of greater than 360 degrees is desirable.